Valve with adjustable weight for automatically varying the moulding pressure in tubemoulding machines



Unit States P t VALVE WITH ADJUSTABLE WEIGHT FOR AUTO- MATICALLY VARY ING THE MOULDING PRES- SURE IN TUBE MUULDING MACHINES Dante Coliiva, Milan, Italy, assignor, by mesne assignments, to Eternit Societa per Azioni, Genoa, .Italy With the usual machines for forming tubes from fibrous suspensions, bestos of the kind described in U. S. Patent No. 1,627,104, operation is merely mechanical: as the thickness of the tube being formed increases, the mobile assembly carrying pressure rollers in contact with the tube is lifted, a cord is connected to the mobile assembly and is tensioned by a counterweight rotating a lever which controls the release pressure of a safety valve interposed in a pressure fluid system for actuating the mobile assembly with the result that the pressure applied by the rollers to the tube is varied. mission which owing to the long and complicated and only moderately accurate. Moreover, to make the above described mechanical control more accurate, the stroke of the lever is utilized entirely only in maximum thickness of the tube, while the mobile assem bly has a much larger stroke for the different diameters of the tubes which may be formed in the machine, as well as for the stroke necessary to lift the assembly during removal of a formed tube. This condition obliges the operator to detach the lever from the cord by means of a handwheel, which actuates a friction clutch every time the mobile assembly is lifted to permit removal of the tube; and to attach it again at the beginning of each tube forming operation. This makes it necessary to accommodate the clutch apparatus directly on the general control board (because else two operators would be necessary) and, therefore, the said board has to be in turn located in a position which may otherwise be inconvenient.

The present invention provides a new solution of the problem of varying the pressure applied by formed which solution completely eliminates any mechanicalconnection to the mobile assembly and is based solely on the uniform variation of the pressure applied by the rollers during a predetermined moulding time. The moulding time of a determined type of tube (that. is, of a tube having a determined diameter and a'determined thickness) is indeed a constant; moreover, the forming pressure has to vary linearly with the thicknessand since the increase of thickness is uniform in time, also the variation of pressure becomes uniform in time. 7

The device according scribed with reference wherein:

Fig. 1 is a diagrammatic representation of a control to the present invention is deto the accompanyingdrawing,

device embodying the present invention and associated.

with a tube forming machine of the described character; Fig. 2 is a fragmentary, enlarged diagrammatic View of a portion of the control device of Fig. l; and

Fig. 3 is a sectional view taken along the line 3-4 of Fig. 2.

tReferring to the drawings in detail, a tube forming machine of the kind described above is thereseen to inin particular tubes of cement asr.

This method requires a mechanical transprevailing conditions is rather the stroke corresponding to the actual plotted the scale of pressures along which two end-of- L The steps L1 and L2 clude a mandrel R on which a tube S is being formed. A back-up or supportng cylinder R1 is disposed below the mandrel in rolling contact with the tube S and serves to support the mandrel and the tube being formed on the latter. A mobile assembly T is vertically movable above the mandrel R and is provided with rollers which contact the tube being formed and serve to compress the material of the tube. The mobile assembly T is suspended from a piston U which is movable within a vertical cylinder V. It is apparent that the pressure of a hydraulic fluid admitted to the cylinder V above the piston U will determine contact pressure or compressing force of the rollers of the mobile assembly T against the tube S being formed on the mandrel R.

Pressure fluid is supplied to the top of the vertical cylinder V through a pipe or line 0, and the pressure of the fluid in the line 0 is controlled by a pressure release or safety valve B. The pressure at which the valve B opens, and therefore the pressure existing in the line c, is determined by the value of the downwardly directed force exerted upon the stem of the valve B by a lever C which is pivoted, at one end, upon the casing X of the pressure release or safety valve. The downwardly directed force exerted by the lever C upon the stem of valve B is determined by the position of a weight A along the length of the lever C. Accordingly, movement of the weight A along the lever C, from right to left, as viewed in Fig. 1, during a tube forming operation, will result in the gradual reduction of the pressure of the fluid in line 0 and in cylinder V thereby to gradually reduce the pressure exerted by the rollers of assembly T against the tube Sas the latter is gradually built up upon the mandrel R.

In accordance with the present invention, the movement of the weight A along the lever C is governed by a slider D to which the weight A is connected. The slider D has a collar-like portion D2 which fits loosely on an elongated screw E having its opposite ends journalled in suitable fixed support members m1 and m2. The collarlike portion has the upper portion of its inner surface formed with an arcuate cross-section and sector threads D1 thereon, as shown in Figs. 2 and 3. Compression springs D are interposed between portion D2 of the slider and a vertically immovable portion D4 of the latter, thereby to yieldably urge the collar-like portion D2 downwardly for engaging sector threads D1 with screw E. However, the collar-like portion D2 of slider D is movable upwardly relative to screw E, in a manner hereinafter.

tained in the position shown in Fig. 1 so as to present no obstruction to the flow of pressure fluid from the line 10a, through the valve P and line 10b to the motor F. The speed of the motor F is controlled by a valve G interposed in the line 10a and adjustable by a knob H, and the adjustment of the motor speed is indicated on a suitable gauge 1' which is connected, in any conventional manner, to the rotated member or part of the motor F.

To make the adjustment of the machine practicaLthe indicator 1' does not indicate the speed of the motor F in revolutions per minute, but it is graduated in such a manner that it indicates automatically the time required for the system in order to make t valve B vary by 1 kg.

The device also comprises a rule Z whereon there is stroke stops L1 and L2 are slidable.

e pressure of the safety .3. are respectively mounted on the screws 1 and 1 supported rotatably by the supports m and m and are held against rotation so that turning of said screws 1 and Z adjusts the positions of the stops L1 and L2, respectively, along the scale or rule Z.

There is also provided a rod 1' parallel to the screw E and fixed in the side supports s, and s Said rod r has a cylindrical enlargement n, which acts as a fixed plunger within a movable hydraulic cylinder M sliding thereover. Said hydraulic cylinder is provided with an extension w terminated in a fork n embracing but not engaging the screw E and has a cam-profiled foot adapted to cooperate with a member g secured to the slider D for the purpose of lifting it and disengaging the segment D1 from the screw E (Fig. 2). The end-of-stroke stops L1 and L2 limiting to the left and to the right the extreme positions of the weight A, establish automatically the maximum and minimum adjusting pressure of the safety valve B and, hence, establish the maximum and minimum moulding pressures applied by the rollers of assembly T against the tube S being formed. The positions of these end-ofstroke stops are adjustable by means of manipulation of knobs L3 and L4 on screws 1 and Z respectively.

The return movement of the slider D into the initial position of maximum pressure is effected by movement of the cylinder M to the right, as viewed in Fig. 1, which movement, as shown in Fig. 2, disengages the threaded sector D1 from the screw E and then drags the whole slider D to the right.

The hydraulic control of the system is effected by a distributor valve N moved by the lever O which has three positions: central, O1 to the right and O2 to the left. Valve N receives the pressure fluid from a supply line 11 and is operative, depending upon the position of the lever O, to direct the pressure fluid either to-a line a or to a line b. When the lever O is moved-to the position 01, the distributor valve N directs the pressure fluid from the supply line 11 to the line a. As seen in Fig. 1, the line a communicates with the valve G, which controls the speed of motor F, with the line 0, through which fluid of controlled pressure is supplied to the cylinder V, and.

with a longitudinal bore 12 extending through the rod 1' from the left hand end of the latter and opening into the interior of the movable cylinder M at one side of the plunger it. When the lever O is moved to the position 02 thereof, the distributor valve N is displaced so as to communicate the line a with the discharge line 11a, while the line b is communicated with the pressure fluid supply line 11. The line b opens into a longitudinal bore 13 extending through the rod r from the right hand end of the latter and opening into the interior of the cylinder M at the side of the fixed plunger u opposite from the opening of the bore 12. As seen in Fig. 1, screw Z is movable axially within the supports m and m,, and is connected to the valve member P. A spring 14 acts on the stem of valve P to urge the latter and the screw E to the right to a position in which the valve P is open. When the screw [1 and the valve P are displaced to the left, from the position shown in Fig. 1 and against the action of the spring 14, valve P is closed to interrupt the supply of pressure fluid to the motor F.

Any time the dimensions of the tube being formed are changed (either diameter or thickness, or both), the controls have to be adjusted for the new work. Three parameters have to be adjusted, namely:

(a) The value of the maximum pressure at the start of the forming of the tube, and this is obtained by displacing the end-of-stroke stop L2 until its pointer coincides with the mark of the desired pressure on the scale Z.

(b) The value of the minimum pressure, which adjustment is effected by displacing in an analogous manner the end-of-stroke stop L1.

(0) Since the total pressure drop p is fixed and the forming time t is known, the unit time of pressure variation (that is the time which in that determined adjustment is required to make the pressure of the valve B vary by 1 kg./sq. cm.) is=p/t. The knob H is actuated to position the pointer of the indicator I at the corresponding unit time value.

Operation is as follows:

Forming is started from the beginning of an individual operation by manipulation of the handle or lever O to position 01. Then the distributor is positioned so that the tube a is put under pressure, with the result that the motor F turns at the predetermined speed and the cylinder M is moved to the end-of-stroke position completely to the left.

The motor F drives screw E and thereby causes displacement of the slider D at uniform speed from the right to the left to gradually reduce the release pressure of valve B so that the pressure in cylinder V and hence the force exerted by rollers of assembly T are gradually reduced until slide D strikes against the end-.of-stroke stop L1, causing axial translatory movement of the screw 1 on which that end-of-stroke stop is engaged, with the result that distributing valve P is displaced to the left, as viewed in Fig. 1, thereby to interrupt the flow of pressure fluid to motor F and halt the latter.

At this time the tube is formed and the operator moves the lever O to the position 02, thereby causing distributor N to connect the tube a to discharge and the tube b to pressure, which causes displacement of the cylinder M to the right and return of the slider D to the starting position against the end-of-stroke stop L2.

What I' claim is:

1. A device for varying the pressure of a fluid in a line; said device comprising a pressure release valve adapted to be interposed in the line so that the release pressure of said valve determines the pressure existing in the line, a lever connected to said valve and urging the latter to its closed condition, a weight slidable along said lever to vary the force exerted by the latter against said valve, means for displacing said weight along said lever including a rotatable screw extending substantially parallel to said lever, a slide connected to said weight and a threaded sector on said slide threadably engageable with said screw, constant speed motor means connected to said screw and effective to rotate the latter in one direction thereby to cause movement of said sector and slide in one axial direction along said screw so that the-weight moves along the lever in said one axial direction at a uniform speed and the release pressure of said value changes at apredetermined rate, and means operative to disengage said sector from said screw and to effect movement of said slide, sector and weight axially along said screw in the opposite direction.

2. A device according to claim 1; further comprising means for limiting the movement of said slide in said one direction along the screw, and means operative when said slide reaches the limit of its movement in said one direction to interrupt the operation of said motor means.

3. A device according to claim 1; further comprising first and second stop members cooperating with said slide to limit the movement of the latter in said one direction and opposite direction, respectively, a support rod carrying said first stop member and movable in the direction parallel to said screw, valve means connected to said support rod to be operated by movement of the latter, said valve means being normally open and being urged to a closed condition by movement of said support rod in said one direction in response to engagement of said slide with said first stop member, and pressure fluid supply means having said valve means interposed therein to interrupt the supply of pressure fluid when said slide reaches the limit of its movement in said one direction as defined by engagement of the slide with the first stop member, and wherein said motor means is pressure fluid actuated. and connected to said supply means so that rotation of said screw is stopped by engagement of said slide with said first stop member.

4. A device for varying the pressure of a fluid in a line; said device comprising a pressure release valve adapted to be interposed in the line so that the release pressure of said valve determines the pressure existing in the line, a lever connected to said valve and urging the latter to its closed condition, a weight slidable along said lever to vary the force exerted by the latter against said valve, means for displacing said weight along said lever, pressure fluid operated motor means actuating said displacing means so that said weight moves along said lever in one direction at a uniform speed and the release pressure of said valve changes at a predetermined rate, means for supplying pressure fluid to said motor means at an adjustable rate thereby to permit variation of said predetermined rate at which said release pressure of the valve changes, pressure 15 fluid actuated return means operative to displace said weight along said lever in the other direction, and control means for alternately permitting the supply of pressure fluid to said return means to operate the latter and to said means supplying pressure fluid to said motor means.

5. A device according to claim 4; further comprising normally open shut-oif valve means interposed in said means for supplying pressure fluid to the motor means, stop means operative to define a limit for the movement of said weight in said one direction, and means actuated by the operation of said stop means to close said shut-off valve means thereby to halt said motor means and stop 10 the movement of said Weight in said one direction.

References Cited in the file of this patent UNITED STATES PATENTS 659,263 Smith Oct. 9, 1900 2,050,020 Schmidt Aug. 4, 1936 2,505,887 Edison May 2, 1950 2,590,503 Brownstein Mar. 25, 1952 

